Method and apparatus for expanding perlite



E. D. ZORADI l METHOD AND APPARATUS FOREXPANDING PERLITE Filed Feb. 21,1948 July s, 1952 s sheets-shear 1 ATTORNEY July 8, 1952 E. zoRADl2,602,782

` METHOD AND APPARATUS Foa ExPANnINc. PERLITE Filed Feb. 21,'1948 :ssheets-sheet z DUST SEPARATOR HoPPER PREHEATER HoPPER l ,an

Fl G. 2

0 n n Feen HoPPr-:R

`PAIFFING KILN NVENTOR ELKO D. ZORADI BY MMW- ATTORNEY July 8, 19.52 E.D. zoRADl v 2,602,782

` METHOD AND APPARATUS von EXPANDING PERLITE Filed Feb. 2'1, 194s ssheets-sheet s PERLITE MRTIGLES INVENTOR AELKIO D. ZORADI ATTORNEYPatented July 8, 1952 METHOD AND APPARATUS FOR EXPANDING PERLITE Elko D.Zoradi, Portland, Oreg., assigner to Dant & Russell, Ine., Portland,Oreg., a corporation of Delaware Application February 21, 1948, SerialNo. 10,013

8 Claims. (Cl. 252-378) My present invention relates to the art offorming a light weight material for use, by way of example, as a plasteror concrete aggregate, a filler for acoustical and insulating purposes,a soil lightener or Conditioner, aggregate for acoustical tile and thelike, and many other useful products, by expanding graded particles of amineral known as perlite. This mineral is mined in several localitiesincluding the State of Oregon and has come into considerable usage inrecent years in various fields of industry. The present invention is acontinuation in part of the invention disclosed and claimed in mycopending application, Serial No. 664,681, filed April 24, 1946, nowabandoned.

The principal object of the present invention is to provide a method andapparatus whereby perlite particles are expanded from five to twelve,preferably about eight to ten, times their original volume in suchmanner that each particle is individually puied to form a popcorn-likegrain having numerous air cells defined by walls of siliceous material,the product being characterized by having considerable resistance tocrushing in handling, shipping or mixing with other materials.

A further object of my invention is to provide apparatus in which myimproved method may be employed and in which the expansion of perliteparticles is uniformlyaccomplished without having the puffed particlesthereafter fuse into solid spheres of material. A general object of thepresent invention is, therefore, to provide an effective and efficientprocess for expanding perlite.

A further object of my present invention is to provide a method forcreation of expanded perlite whereby the formation of undesirable nes(noncellular particles resembling dust or fine powder) is avoided, whichmethod is economical not only in that the resulting product'is uniformwithin permissible limits and does not require screening to removefines, but in that waste effort and expense of crushing, transportingand further treatment of portions of a perlite ore mass, which by priorart methods formed nes, are avoided.

A further object of the present invention is to provide a method andmeans whereby continuous operation to produce expanded perlite of aplant once set in motion is brought about, thus permitting economicalproduction. Y

A further object of the present invention is to provide a perliteexpanding plant which is economical in operation and may be operated bya minimum number of workmen.

A further object of the present invention is to provide a plant forproducing expanded perlite 2 wherein all lightweight end products arecaptured for ultimate use ina number of elds of usage wherein ne powdersof the character thus produced may be utilized.

The invention will be more readily understood by reference to thefollowing specification taken in connection with the accompanyingdrawings wherein like numerals refer to like parts throughout, while thefeatures of novelty will be more distinctly pointed out in the appendedclaims.

In the drawings- Fig. 1 is a plan view of a plant embodying myinvention;

Fig. 2 is a side elevation of the plant disclosed in Fig. 1, with someportions broken away;

Fig. 3 is a vertical section taken substantially along line 3 3 of Figs.1 and 4;

Fig. 4 is a vertical section taken substantially along line 4 4 of Figs.1 and 3;

Fig. 5 is a vertical section taken substantially along line 5 5 of Figs.l and 6; and

Fig. 6 is a vertical section taken substantially along line 6 6 of Figs.1 and 5.

The present invention may best be. understood by describing the processrst, after which the particular equipment embodying my invention will bedescribed.

PTOCGSS Perlite, which is a grey to greyish-black, volcanic, glassy,non-metallic rock, is essentially an impure silicon-aluminum oxide. theprincipal impurities usually being oxides of iron, sodium and potassium.In the raw or natural state rocks of the perlite type contain from abouttwo to about seven, with true perlite containing from about three toabout four, per cent by weight of combined water. Perlite is a rhyoliticglass as distinguished from obsidian which is a basaltic glass havingless than about 0.5 per cent water of crystallization, .usually none oralmost none. The above percentages of water of crystallization are byweight. When perlite is ground or otherwise pulverized or comminuted andsubjected to a temperature of from about 1200" F. to 2500 F., and highertemperatures, for a short period of time depending on the particle size,the particles are rapidly brought to the melting point and expansivegases generating internal pressures are created, causing the particlesto expand `to several times their original volumethe amount of expansiondepending upon certain factors as will appear. The expansion or puing ofthe particles lis achieved when theparticles are brought to theirmelting temperature rapidly and rendered plastic form expansion to abouteight toten times the original volume, the product weighing about eightto twelve pounds per cubic foot. I can control the process to achieveweights ranging .from about six pounds per cubic foot to fteen or twentypounds per cubic foot; but in the first instance the degree of expansionis so great that the walls of the cellular bodies are too fragile andbreak down under plastering pressure or other handling, and in the lastinstance the amount of expansion is not sufficient'to assure thehighestvalue in thermal insulation, acoustical insulation, sound deadening, andother properties. When expanded to about eight to twelve poundsper cubicfoot the resultant product is a white or light-colored materialconsisting substantially of a multitude of minute hollow cells ofsilica.

Perlite Vin commercial quantities appears in veins or buried masses'withcrystalline lavas and other impurities penetrating the outer layers. Thepercentage of water of crystallization in a single vein or mass may varywidely from place to place. In one large mass with which I am familiar,having a depth of about vone hundred fifty feet, the upper layer of. theperlite` ore contains about five toseven percent water ofcrystallization to a depth of several feet from the top surface, themain mass of the ore ranges from about three and one-quarter to four percent water of crystallization, and the very bottom few feet'containabout three per cent water of crystallization.

I have found that the degree of expansion vof perlite-particles dependsto someextent `upon the temperature a't'wliich` expansion is effected,to

some extent upon the amount of water of crystallization in theparticles, to some extent upon the sizes of the particles, and to someextent upon other factors as will presently appear. It is an importantstep in my process to analyzethe perlite or'e for water ofcrystallization in order that all 'portions thereof having less thanthree percentwat'er of crystallization may be rejected, sinceV suchportions will not react to the heat treatment in a satisfactory manner.

I nV order to determine the percentage of water of crystallization asample of the Vperlite is crushed to the desired size, placed in a drierat 240 F. for one hour, until thoroughly dried of all'surfaceor'capillary moisture, and a tenlgra'm l sample is segregatedtherefrom.This sample is weiglied,'then brought to 1200 F. in a mufrle for onehour. The difference in weight before and after subjecting to this hightemperatureis'the weight-of the water of crystallization.

I have also determined that if more than about four'a'nd'one-half percent by weight oflwater of crystallization is present the perlite ismore siliceous and has a lower melting point so that it requires` lessheat to melt particles of'a given size, and also'the resulting product'is shattered or exploded to such 'an extent as to be toofragile ortooYfine for'most purposes; forexample, a certainsizeparticle of perlitewill be properly melted to' a plastic state at 2500 F. if it containsthree with my disclosure.

and one-half per cent water of crystallization, but if the samplecontains four and one-half per cent water of crystallization atemperature of 1800 F. is all that is necessary properly to melt theparticles. Similarly, I have found that variations in amount of certainimpurities cause variations in the melting temperature, but to a lesserextent than variations in the amount of water of crystallization. One ofthe impurities which may be removed is clay which is formed in thecracks between the small, solid masses of the ore. This clay is visibleto the naked eye as fine lines or jagged streaks. An important part ofmy process is to crush the ore and, while grading it to maintain acertain maximum and minimum size limit, to wash the clay dust out of theperlite ore. If the clay is permitted to remain with the perlite ore itwill to a certain extent cause fusing together of expanded particles,rendering the end product unfit for use. This result is due to therelatively low melting point of clay.

Accordingly, important steps which should be followed in producingexpanded perlite are to analyze the ore for water of crystallization andretain only those portions having between three and four per cent byweight water of crystallization, to comminute the retained ore and gradeit as 'to size, and to wash the comminuted ore t0 remove dust whichv isprincipally clay from the cracks occurring in the veins of the ore.

The next step in my process is to dry the washed particles so thatuniform conditions may be maintained in the puffing apparatus. Theparticles are dried before being subjected to puffing temperatures insuch manner as to remove free water therefrom. Drying is accomplished bysubjecting'the particles to heat while shielding themfrom direct flameor high temperatures.

The degree of expansion of the particles depends somewhat upon thetemperature at which expansion is eiiected. For medium size particles acertain temperature is satisfactory, for larger particles a highertemperature, and for smaller particles a lower temperature. Thetemperature, however, cannot be too easily controlled; hence Iflt theparticle size to the temperature of the flamev produced by standardfuels. Preferably, I expand'perlite in a propaneair mixture having aYflame temperature of about 2500 F., and I have` determined thatparticles graded to limits of minus twenty screen mesh to plus onehundred Viifty'sc'reeii mesh'uniformly pop to about eight times theirvolume in this temperature when other'conditions are controlled inaccordance If a higher percentage of fines is desired the limits may bealtered to minus thirty mesh to plus one hundred fifty mesh.Various'other fuels may be employed, such as oil-air mixturesand variousmixtures of gases and air Vsuch as'manufacturers gas, producers gas,vo'rthe like. All such flames will produce a dame temperature of about2500 F. or higher, and-the particle size and the number of particles'per unit of ltime injected into the ame may be varied so as tomaintainuniformity of the puffed product.' When I speak of a flametemperature of 2500 F. orhigher, it should be realized that the term isnecessarily indefinite because of the variability of the caloriiic valueof the fuel and theproblems inherent in maintaining an even fuel-airmixture. Observations taken over several years prove that the bestresults are obtainedlwith a fuel mixture having a theoreticalnametemperature of 3200 F. The area of flame contact with the perliteparticles when using such a fuel is consistently measured with anoptical'. pyrometer as having a temperature -of 2500a F.,l

with 'occasional fringe spots and. variations up to 2800 F. The loweringof the mean temperature from the theoretical temperature .is undoubtedlydue to the cooling effect of the introduced perlite, and localvariationsr-or variations from time to time are dueto variations in thefuel, the fuel-air ratio, variations in the composition of :the perliteand its free water, and irregularities. in feeding the perlite into theflame. 1

It is an important step in my process that the ame zone into which theparticles are projected be maintained at 2500 F., or approximately thesame, for ore of three to four per cent water of crystallization, andlower for higher percentages of water, which requires balancing of thequantity or mixture of the fuel, the quantity of secondary air admitted,andthe quantity of particles admitted. The maintained temperature couldvary, but a considerably higher temperature would fuse puffed particlestogether, all other conditions being equal, and a lower temperaturewould calcine or desiccate some particles. I have determined thatdehydration accompanied by a minimum degree of expansion takes placewhen particles of about one hundred fty meshA are subjected totemperatures below 1200 F.; when quickly heated to l500 F. they areexpanded to about five times their original volume; while at 2100" F.they expand to between nine and ten times their original volume. If,however, these ne particles are included among larger particles up totwenty mesh the same amount of expansion takes place at highertemperatures so that 2500 F. flamev temperature or heating zone.temperature appears to be essential. If the larger particles alone aresubjected to temperatures of about 1200 F. hardly any expansion takesplace but the` particles will desiccate or calcine; when quickly heatedto around 2000? F. they expand iive or six times their original volume;andwhen quickly heated to 2500 F. they puff to the desired eight to tentimes their original volume. Thus when particles graded between thedesired limits are subjected to temperatures of 2500 F. they produce anendproduct having eight to ten times the original volume and a weightrof about eight to twelve pounds per cubic foot.

Gradual dehydration of the particles must be avoided, since suchdehydration results in the water of crystallization escaping slowlywithout forming expanded cells in the particles. On the other hand, itwould do no good to rapidly form gasesincluding steam from the waterV ofcrystallization if the perlite particles were ,not brought to themelting temperature. I have determined that a temperature of about 1200F. is the low limit of melting of fine particles of perlite ore such asone hundred fifty mesh, and 2500 F. may be necessary to melt largerparticles such as twenty mesh. A graded mixture as above melts uniformlywhen air-borne at temperatures of 2500 F. The two actsl of forming gasesand fusing the. silicate must take place simultaneously so that theinternal pressure of the gases can createy spherical cells. of meltedsilicate. However, if the particles are allowed to remain in a meltedstate longer than an instantaneous interval of time and come in contactwith each other ina melted state the particles will fuse together intoYsolid-frnasses t of glassy material. Therefore, an important step in theprocess is to remove the puiedparticles from the vmelting temperature-zonef immediately upon Vformation of the puffed particles. Variousmeansmaybe lemployed Vfor creating a melting` zone of limited extent,and various meansA may' be employedv quickly to remove the expandedparticles from the melting zone; for fexample, air, nitrogen or othergas inert to melted perlite maybe heated and projected as a blast of hotgas to which the perlite is subjected, therhot gas being drawn off underforceddraft of. suicient velocity -to float thepuffed particles -athighl ingv atl 2500OA F.- or higher, and the flame being.

underv forced draft so that the products of combustionare drawn from thehottest zone atsuch high velocity as to float the puied particles andconvey Vthem to cooler regions.v VAt. a `region where-the temperature isat or below 1800"i`F.`

the velocity of the products of combustion is reduced and preferably thedirection thereof changed so that puffed particles drop from theconveying blast. At this point the vparticles are belowthe fusingtemperature thereof and will not `stick to each other or to the walls ofthe furnace or the like, or be reduced to solid spheresbysurfacetension. Y

A further point which I have discovered is that the direction and mannerof injection of perlite particles into the flame or hot blast isimportant. I prefer to inject a thin sheet of the particles-atrelatively high velocity, such as by propelling them dispersed in ablast of compressed air, directly into the hottest portion of the flame,atv right angles to the direction of the llame. If the particles arepropelled into the flame in the direction of the blast most of thelighter particles will be shot from the hot expanding zone beforesufficient expansioncan occur and the steam will escape harmlessly,leaving a calcined or desiccated `product which will either remain as ahard grit or will break into a ne powder. If the directionof propulsionis substantially coincident with the direction of the flame very littlepuffing will be accomplished.l The higher the angle of incidence thegreater the efficiency becomesv until the maximum percentage of expan-4sion of particles takes place when the angle of incidence is ninetydegrees or greater. No advantage is achieved by having an angle of-incidence greater than ninetyy degrees, since valthough more expansionmight take place finer particles might not be propelled directlylthrough the flame inthe event they are not puffed immediately and wouldbe turbulently carried around in the flameA zone until fused solidlytogether. Therefore, I prefer to have the injection take place at anangle of ninety degrees and preferably directed downward through ahorizon-.- tally directed ame so that all particles which do not puffimmediately Yupon contact with the flame are shot to the bottom of theiame chamber below the point of contact which mayv be maintained at atemperature below 1200 F., the point at which the ner unpuffed particlesfuse together.`

I have determined that the major proportion of the particles arepufiedon the rst passage throughthe flame, but a considerable percentage,particularly of `larger particles, will shoot through the flame withoutbeing puffed. I collect these` particles and ,elevate them through azone having a temperature of less than 1200o F. to a point above theflame from which they are dropped through the name. Most of suchparticles are puffed on the second contact with the flame. v Y

A specific apparatus for carrying out the process of the presentinvention will now be described, the preferred embodiment thereof beingillustrated in the accompanying drawings.

I prefer to use a horizontal, rotating drum kiln, the interior of whichis substantially three feet in diameter by ten feet long with the actualflame confined to the axial portion of the drum and to a length of aboutsix feet or less from one end., The burning fuel is injected at one endand the ore particles are blown into the hottest portion of the ame zonevin`a thin sheet at a rate such that the desired temperature conditionsare maintained.V Air to support combustion is admitted as primary airmixed with the fuel, and as secondary air flowing through small openingsadjacent to the burners which extend into one end of the drum, the endof the drum being substantially sealed by a shield so that control ofthe draft may be achieved. Some secondary air is also admitted throughthe particle injector. Forced draft is induced by a mechanical blower atthe far end of ythe apparatus at a rate such that a negative pressure ofone and three-tenths to one and six-tenths inches of water is maintainedin the kiln, sufficient to cause movement of the expanded particles fromthe kiln to a separator at the end of the kiln in about five seconds orless. However, the horizontally directed flame blast is such as topropel the light, puffed particles from the name itself substantiallyinstantaneously. When pure butane or propane is used as a fuel thetheoretical flame temperature is about 3850o F., but the preferred fuelis either of the above gases mixed in certain proportions with air tocreate a mixture having a theoretical flame temperature of 3200" F. andan actual ame temperature of about'2500" F., due to the cooling effectof the injected perlite. I find that controlling the rate of fuel feed,or the rate of secondary air admission, or the speed of an exhaust fan,or the rateof introduction of the perlite particles into the flame, orany combination thereof i so as to maintain a temperature of about 1800F. at the outlet end of the rotating drum, achieves the best results.Under the conditions stated the expanded particles are air-borne andreach a cooler region of the drum before they can be fused togetheroriformed into solid glassy particles by surface. tension. This is notonly important in Yorder that the particles may be uniform but isextremely important to successful plant operation. If for any reasonfusing together occursV while the particles are air-borne, deposits ofVglassy material soon build up in the kiln or separator andthe plant mustbe shut down while linings are replaced or deposits chipped o. Sincefrom one to three days are required to permit suiicient cooling tooccur, it is readily understandable that fusing is costly. In accordancewith my process and when it is carried out in my apparatus asdescribedsuch fusing is substantially eliminated.

As a further step, the kiln dischargesinto air separators where the nesare separated from the heavier puffed particles and' each is separatelybagged for use in its own field, or the two may be mixed in variousproportionsfor some purposes.

nhs

' Expanded perlite made in accordance with the foregoing processconforms with the standard specifications of the American Society forTesting- Materials for sand screen analysis of plaster sand, which areas follows:

Percentage Retained Retained on Sieve Maximum Minimum N o. 4(M60-micron) .4.; 0 N o. 8 @S80-micron) l0 0 No. (590-micron) 80 15 No.(297micron) 95 70 N o. (M9-micron) 95 Ther amount of material finer thana No. 200 VT4-micron) sieve, shall not exceed ve per cent.

The sieves shall conform to the'requirements of the StandardSpecifications for Sieves for Testing Purposes (A. S. T. M. DesignationE11) of the American Society for Testing Materials.

Apparatus Thepreferred apparatus 'for carrying out the method of theinvention comprises an elevated platform I0 which may be reached by aladder I I. Mounted upon the platform I0 are a preheating -kiln I2 andan expanding or puffing kiln I3, details of which` will be describedbelow. The crushed or otherwise comminuted perlite, graded and washed aspreviously described, is fed into an inclined preheating kiln through achute indicated by the numeral I5. The preheated particles drop from thelower end of the kiln I2 into an end bellI Ev which feeds into a hopperIl having a passage I8 extending therefrom. Any suitable type of'elevating mechanism (not shown) may be provided to take the materialfrom the lower portion of chuteIS to its upper end at a considerableheight above the puing kiln I3 where the material is deposited ina largehopper I9'. The material travels through a chute 20 from the bottom ofhopper I9 into an injector which extends into the pufng kiln I3 wherethe particles are subjected to heat under controlledv conditions. Thepuffed particles are ejected from the kiln I3 into the upper left halfof a large, covered hopper 22 which has a heat reflecting wall oppositethe mouth of the kiln and which is provided with an intermediate baiile23' extending downward from the top wall to a point below the lower edgeof the kiln I3, the baille preferably having an arched lower edge asshown by dash lines in Fig. 2. The large size of the hopper permits thegases to reduce their velocity and cool by expansion suiilciently todrop the floating particles, this action being aided by the changes indirection of flow. A duct 26 communicates with the top of the hopper 22at the right side of the baffle 23 and opens in to a suitable dustseparator 21 having an airtight dust ejecting valve 28 at the lower endthereof. The outlet of the separator 21 comprises a duct 29which'extends downwardly into a washing chamber 30-having suitable spraymeans (not hereiny disclosedl for washing any remaining fine dust fromthe gases passing therethrough and to cooljthe gases before they contactthe blower.

- washed gases to the atmosphere thorugh a fiue 35.

Puied particles which ow from the puiiing kiln i I3 drop into the bottomof hopper 22 and may be removed therefrom through an airtight valve 36.The valve 36 preferably comprises a housing enclosing a revolvablepaddle wheel 31 having its projecting vanes adapted to bear against apair of curved plates 38 whichare pressed against the ends of the vanesby springs 39. Material which is caught in the pockets between vaneswill be carried past the plates 38 and dumped through an outlet 40shaped to enter the mouth of a sack or the like. The wheel 31 may berotated by any suitable means, and sacks or other containers may beassociated with the outlet in any suitable manner. It is only importantthat the valve 36 be capable of ejecting the material without permittingingress of any air. The valve 28 is preferably of similar character andis adapted to eject ne material into containers without permittingingress of any air. Thus the draft which is created by the blower 32extends through the washer 30, iines separator 21, solids separator 22and kiln I3 to the burners.

In order that the finely crushed material may be thoroughly driedwithout subjecting the material to flame, and in order to increaseefficiency and cause uniform feeding and temperature control to result,the preheating kiln I2 preferably comprises a large cylindrical drumset-on an incline from right to left. The upper end of the kiln isprovided with an end wall 45 having av central opening therethrough intowhichv .the chute I extends, there preferably being provided astationary sealing member 11B-having a flange overlying the flangeprovided by the end wall45. The drum is provided with a pair of bearingrings 41 rolling on pairs of spaced rollers 48 mounted upon suitablejournals extending upward from the platform I0. A thrust bearing. may beprovided by means of a substantially horizontalwheel 49 bearing againstthe lower side of' one of the bearing rings 41. The drum issurroundedvby a large gear 58 meshing with a pinion `5I'driyen throughreduction gear means 52 by a motorV 53. The lower end of the drum I2extends into a stationary sealing ring 54 -provided at the'side of theend bell I6. The drum is provided' with a plurality of longitudinally.extending interior ribs 55 upon which are mounted a plurality of struts56 extending inwardly to support a central, Vcoaxial flame tube 51. Theflame tube isopn atV both ends, the upper end Vterminating short. of andabove the outlet of chute I5 and the lower end extending through theendbell I6 into a nrebox 58. The firebox is filled with the burningproducts of combustion ejected thereinto fromv suitable means such asthe gas burner 59 herein indicated. The products of combustion emergingfrom the upper end of the tube 51 reverse direction and flow backbetween the tube 51 and the outer shell and pass into the end bell `I 6.1 The upper end of end bell I6 communicates a one side with a duct 60which is open to the atmosphere and may lead from a point outside of theplant so as to permit the introduction of cool fresh air. At theopposite side of the upper end of end bell I6 a duct 6l communicateswith the lower end of a dust separator 62. The dust separator preferablycomprises a conical lower extremity 63 having a suitable clean-out valvetherein (not herein detailed) into which the duct 6I z extends.

Gases passing thereinto pass upward through a central cylinder64-risingalmost to the imperforate top of the outer cylinder forming theshell of the collector 62 and then pass downwardly between theinner andouter cylinders. A vduct 65 communicates with the bottom of this spaceand extends into the inlet of a blower 66, driven by a :motor 61, whichforces the gases outwardly through an exhaust duct 68.`

j- `By the use of such a preheatingkiln the ore particles may bepreheated to thedesired temperature without coming into contact with ameor burning material since combustion is entirely completed` in the rebox58 and the long tube 51. The particles may thus be thoroughly dried butat the same time are not subjectedto heat linsuch a manner as to causecalcination thereof. The consumed hot gases passthrough the spacebetween the inner and outer tubes in contact' with vthe particles ofmaterial which are being'sifted through the gases by the longitudinalribs 55.

The hot gases, bearing some dust particles, will be cooled by the airentering through duct 60 and the dust will be separated in the separator62. The dust collected in the' conical tip 63 may be kept for somepurposes or removed to a waste heap. The hot particles are elevatedintov the hopper I9 and are then subjected to direct flame in thepuffing kiln.

The purpose of preheating the particles is to increase the over-allefficiency of the plant vand to dry the 'particles so that they willflow' evenly and many particles will calcine or fail to puff.

The pufiing kiln preferably comprises a large,

inclined drum 10 having a narrow annular flange 1I at its outletend'anda wide annular flange I2 at its inlet end. The inner surface ofthe drum 10" may be lined with a suitable ceramic lining 13 or otherinsulating material upon which are laid a plurality of fire bricks 14,certain courses of which project inwardly to form longitudinal ribs 16.The flanges 1I and 12 provide means to retain the lining and bricks inposition while flange- 12 serves further to provide a sealing ring toride against a baille plate 11 surrounding the. burners and throughwhich the injector projects. The shell 10 is provided with a pair ofbearing rings l80 each adapted to rest upon a pair of supportingwheelsSI mounted on a frame supported by the platform I0. The lower-ring 88 bears against a horizontally disposed wheel 82. A centrallydisposed gear 84 meshes with a pinion 85 driven by a motor 86 through areduction gear box 81. `The kiln thus continuously rotates to permit theribs 16 to pick up any particles which may not have been puffed lwhilepassing through the ame zone and cause`r them to drop through the heatedgases. The distance of the walls of the puing kiln from the flame Zoneis such that the temperature thereof surrounding the point of contact ofthe particles with the iiame is maintained preferably below v0 F. andthe speed of rotation of the kiln and the number of ribs is such thatthe particlesY capable of puffing on second or third passage through theflame are not fused while being elevated, or

.desiccated without having a chance to become puffed. The incline of thekiln and the force of the flame helps in distributingV the elevatedparticles evenly along the line of the flame so as to avoidconcentrations of elevated particles in the region of injection of thefresh particles.

.A plurality of burner nozzles 90 project into the inlet end of thekiln, the number of nozzles and the location thereof being selected sovas to create a centrally disposed, longitudinally directed flame zonein the first third of the kiln. The nozzles are preferably such as tocreate a` combustible mixture of a fuel such as producer gas, butane,propane or the like admitted thereinto through a supply tube 9|controlled by valve- 92, and air admitted through a supply tube 93. 'Ihedetails of such Valves and nozzles are not herein disclosed, as manysuch valves and nozzles are available. The baille plate 'l1 is providedwith openings 94 adjacent the nozzles 90 for the admission of secondaryair.

The preheated particles of perlite are admitted to the flame zonethrough a spreader 95, into the top outer end of which the particles areadmitted from the chute 20. The particles are projected or forciblysprayed from the spreader by a blast of compressed air admitted througha supply tube 96 having a regulating valve 91 therein. The inner end ofthe spreader 95 is flared laterally and directed downwardly into thehottest portion Vof the flame issuing from the nozzles 90, theconstruction being such that a fan-shaped thin sheet of fine particlesis propelled vertically into the burning fuel. The creation of a thinsheet of particles assures the subjection of all particles to the sametreatment since flame of uniform tempera-ture simultaneously impingesupon all particles. The spreader 95 preferably comprises a turned-downlip at such an angle as to cause the particles of air-borne perliteimpinging thereagainst to project downwardly through the hottest part ofthe flame zone at about ninety degrees to the axis of the flame blast.The valve 91 provides means whereby the amount of perlite fed throughthe flame may be varied. Automatic means may be installed responsive tothe `temperature at the outlet end of the kiln for controlling the draftor the amount of feed or the like, but normally it is suclent toestablish control manually.

Because of the human element involved some fused particles may be formedand collect upon the kiln or the interior of the hopper 22, principallybecause of injection of perlite particles before the ideal operatingtemperatures have been achieved, and secondly because the operator hasno way of knowing whether the draft is sufficient until he'has observedthe resulting actions of the puffed particles. Various conditions ofatmospheric pressure, wind velocity or other factors may affect thedraft so that some particles may be fused from time to time. In order toreplace liningr materials or to permit chipping out deposits of fusedparticles I preferably provide the hopper 22 with an entrance door IDU.

It is to be appreciated that various other forms of apparatus may besubstituted for those herein disclosed, and various modications inarrangement and detail will be readily apparent to those skilled in theart. I claim all such modifications as come within the true spirit andscope of the appended claims as a part of my invention.

I claim:

l. The process of expanding finely divided perlite particles whichcomprises the steps of forcibly propelling dispersed particles ofperlite in a thin flat, fan-shaped compressed air stream directeddownwardly'into a horizontally directed flame having a temperature above2500 F. at the point of contact of the perlite'particles with the flameat which point most of said particles are rapidly expanded, the plane ofsaid compressed air stream being transverse to the axis of the flame,providing a forced draft for said flame whereby all of said expandedparticles are carried with the products of combustion longitudinally ofsaid flame to a relatively cool region remote therefrom, collectingbeneath said flame the remaining unexpanded particles which passtherethrough, and mechanically elevating said unexpanded particlesaround said flame through a zone having a temperature less than 1200 F.to a point above said flame, and dropping said unexpanded particles intosaid flame.

2. The process of expanding perlite which comprises the steps of forminga flame about a substantially horizontal axis, said flame being producedby a mixture of a gaseous fuel and air having a flame temperature above2500" F., creating a forced draft for said flame to maintain rapidtravel of the products of combustion thereof horizontally to a pointremote from said flame where the temperature thereof drops below thefusion temperature of expanded perlite particles, and forciblyprojecting a thin sheet of finelyV divided perlite particles into saidllame in a compressed air stream coming from above and substantially atright angles to the horizontal axis of the flame, the plane of said thinsheet extending substantially normal to the direction of the flame axis,said perlite particles .being introduced into said flame at a pointhaving a temperature above 2500 F. at which point most of said particlesare rapidly expanded, said forced draft being of sufficient strengthrapidly to carry expanded particles in free space from said flame tosaid remote point.

3. A puffing kiln for expanding perlite particles comprising asubstantially horizontal kiln,

. burner means to project a flame of relatively high temperature intoone end of the kiln, and means to inject a thin, relatively wide sheetof perlite particles across the flame, said means comprising a nozzleunit extending into one end of said kiln and having a relatively narrow,elongated discharge opening, said opening extending longitudinally inthe direction transversely of the axis of said flame and directed in adirection substantially perpendicular to the longitudinal axis of saidflame whereby the plane of said sheet of perlite particles projectedthrough said nozzle opening extends substantially at right angles withrespect to the longitudinal axis of said flame.

4. A puffing kiln for expanding perlite particles comprising asubstantially horizontal kiln, burner means to create a flame zone ofrelatively high temperature at one end of the kiln and directedlongitudinally thereof, nozzle means to forcibly inject a relativelywide, thin sheet of perlite particles transversely of the llame zone,

said nozzle means having a relatively narrow, elongated dischargeopening extending transversely of said kiln and directed downwardlytoward said flame zone whereby the plane of said sheet of particlesprojected from said nozzle extends substantially at right angles withrespect to the longitudinal axis of said flame, and means to control thedraft through the kiln whereby puffed particles may be withdrawn inair-borne 13 fashion from the ame zone at a speed such that fusing ofthe puied particles is prevented.

5. Apparatus for expanding perlite comprising a cylindrical kiln havinga refractory lining,

means for rotating said kiln in an inclined position about itslongitudinal axis, means comprising a pressure burner for directing aflame into one end of said kiln along the longitudinal axis thereof,blower means for introducing nely divided perlite into and across saidflame, suction means operatively connected to the other end of said kilnfor withdrawing expanded perlite from said kiln, and longitudinal ribson the inner wall of said kiln adapted on rotation of said kiln toconvey the unexpanded perlite falling tov the bottom of said kiln to apoint above the ilame.

6. Apparatus for expanding perlite into and comprising an inclinedcylindrical kiln, means for rotating said kiln about its longitudinalaxis, a burner having a nozzle extending into the upper end of said kilnand adapted to direct a ame along the longitudinal axis of said kiln,conduit means for directing an air stream carrying nely divided perliteinto and across said flame, said conduit means having a transverselyaring outlet terminating above and in front of said burner nozzle, asettling chamber at the lower end of said kiln of relatively largevolume to permit expansion and cooling of the products of combustion,and suction means operatively connected with said chamber forwithdrawing Vexpanded perlite from said kiln.

7. Apparatus for expanding perlite comprising a substantiallyhorizontal, slightly inclined, cylindrical kiln having a refractorylining, means for rotating said kiln about its longitudinal axis, aburner having a nozzle extending into the upper end of said kiln andadapted to direct a name along the longitudinal axis of said kiln, meansfor injecting a thin, fan-shaped sheet of finely divided perlite intosaid kiln from above and into said ame with the plane of the sheet beingat right angles to the axis of the flame, a settling chamber at thelower end of said kiln and having a substantially vertical wall oppositeand in heat reecting relation to the lower end of said kiln, and suctionmeans connected with said chamber for withdrawing expanded perlite fromsaid kiln into said chamber and the products of combustion from saidchamber.

8. Apparatus for expanding perlite comprising an inclined, cylindricalkiln having a refractory lining, meansV for rotating said kiln about its14 longitudinal axis, a burner having a nozzle extending into the upperend of said kiln and vadapted to direct a flame along the longitudinalaxis of said kiln, means for injecting a thin sheet of nely dividedperlite into said kiln downwardly acros said ame, a settling chamber atthe lower end of said kiln and having a hanging baffle at one side ofand parallel to said kiln and extending below the level of said kiln,and suction means connected with said chamber beyond said baie forwithdrawing expanded perlite from said kiln.

ELKO D. ZORADI.

REFERENCES CITED The following references are of record in the 111e ofthis patent:

UNITED STATES PATENTS Number Name Date 371,715 Sonnet Oct. 18, 1887423,598 Duncan Mar. 18, 1890 920,333 Hughes May 4, 1909 1,456,392Marshall May 22, 1923 1,488,055 Newberry Mar. 25, 1924 1,628,197 RyderMay 10, 1927 1,779,626 Horn et al. Oct. 28, 1930 1,909,820 Falla May 16,1933 1,963,276 Miner et al June 19, 1934 2,021,956 Gladney Nov. 26, 19352,026,441 Shafter et al. Dec. 31, 1935 2,160,956 Cheesman June 6, 19392,265,358 Denning Dec. 9, 1941 2,300,042 Caldwell Oct. 27, 19422,306,462 Moorman Dec. 29, 1942 2,388,060 Hicks Oct. 30, 1945 2,421,902Neuschotz June 10, 1947 2,431,884 Neuschotz Dec. 2, 1947 2,455,666Fournier Dec. '7, 1948 2,501,962 Pierce Mar. 28, 1950 2,505,249 Johnsonet al. Apr. 25, 1950 FOREIGN PATENTS Number Country Date 420,041 GermanyOct. 14, 1925 OTHER REFERENCES Perlite, Source of Synthetic Pumice, Bur.of Mines, pub. IC 7364, Aug. 1946, pgs. 2 and 3.

State of Oregon, Dept. of Geology and Mineral Resources, GMI, ShortPaper No. 16, Dec. 1946, pgs. 10 and 12.

Univ. of Ariz., Bulletin, vol. 15, No. 4, p. 34 (Oct. 1944).

1. THE PROCESS OF EXPANDING FINELY DIVIDED PERLITE PARTICLES WHICHCOMPRISES THE STEPS OF FORCIBLY PROPELLING DISPERSED PARTICLES OFPERLITE IN A THIN FLAT, FAN-SNAPED COMPRESSED AIR STREAM DIRECTEDDOWNWARDLY INTO A HORIZONTALLY DIRECTED FLAME HAVING A TEMPERATURE ABOVE2500* F. AT THE POINT OF CONTACT OF THE PERLITE PARTICLES WITH THE FLAMEAT WHICH POINT MOST OF SAID PARTICLES ARE RAPIDLY EXPANDED, THE PLANE OFSAID COMPRESSED AIR STREAM BEING TRANSVERSE TO THE AXIS OF THE FLAME,PROVIDING A FORCED DRAFT FOR SAID